Electro-conductive material containing pbo and ruo2

ABSTRACT

AN ELECTRO-CONDUCTIVE MATERIAL ESSENTIALLY CONSISTING OF A DOUBLE OXIDE OBTAINED FROM PBO AND RUO2 IN A MOLAR RATIO OF 3:1 TO 1:3, WHICH IS USEFUL AS THE FUNDAMENTAL COMPOSITION FOR PRODUCTION OF A RESISTOR PASTE, A CERAMIC RESISTOR OR THE LIKE.

. w 1973 TORU KASANAMI ETAL 3,

ELECTROCONDUCTIVE MATERIAL CONTAINING PBO AND Rub Filud Dec. 28, 1970 I v 3 Sheets-Sheet 2 FIG, 2

Pb0-Ru02-1/2Ta2O5 PbO-RuO (l l) 680 700 720 740 760 780 800 PEAK FIRING TEMPERATURE (c) 11, 1973 TORU KASANAMI ETAL 3,778,389 E ELECTRO-CONDUCTIVE MATERIAL CONTAINING PBO AND Rut) Filed Dec. 28, 1970 5 Sheets-Sheet O V v I I +Ag ,Pd,Au,[f 680 700 720 740 760 780 800 PEAK FIRING TEMPERATURE (C) United States Patent Office Im. on. H01b 1/06 US. Cl. 252-520 25 Claims ABSTRACT OF THE DISCLOSURE An electro-conductive material essentially consisting of a double oxide obtained from PhD and Ru in a molar ratio of 3:1 to 1:3, which is useful as the fundamental composition for production of a resistor paste, a ceramic resistor or the like.

The present invention relates to an electro-conductive material essentially consisting of a double oxide obtained from UbO and Ru0 and a resistor composition comprising the same.

Hitherto, there has been known an electro-conductive material essentially consisting of RuO In a resistor composition obtained by using such known electro-conductive material with a glass frit, the control of the resistivity can be accomplished only by variation of the content of RuO When the content of RuO is much decreased, however, for production of a resistor composition of high resistance, the content of the crystal component is lessened and a constant dispersibility of the crystal component after sintering is reproduced with great ditliculty so that the resistivity of the resistor composition is considerably varied and madeuneven on each product. When the content of RuO is much increased for production of a resistor composition of low resistance, the content of the glass component available as a binder is necessarily lowered so that it cannot assure the good rigidity of the resultant resistor composition. The resistor formed with such resistor composition shows an inferior tolerance to moisture in atmosphere, from which the change of the resistivity is caused and the life of the resistor is shortened. Thus, the regulation of the resistivity is not freely made without bringing any disadvantage into the material properties. In addition, a large, positive temperature coefiicient of resistivity inherent to RuO appears particularly when the content of RuO appears particularly when the content of RuO in the resistor composition is high. Although such an improvement as incorporating Nb O into RuO to make a solid solution Patented Dec. 11, 1973 tained from PhD and RuO in a molar ratio of 3:1 to 1:3 with or without replacing less than by mol of PbO and/or Ru0 by any other replaceable metal oxide. When the production of high resistance is desired, for instance, less than 50% by mol of RM); may be replaced by Ta O( /zTa O5), so that the resistivity of the electroconductive material itself will be increased. Thus, the content of the electro-conductive material in a resistor composition is not required to make small and, as a matter of course, the defect due to the low content of the electro-conductive material as seen in a conventional resistor composition using the electro-conductive material consisting of RuO alone is overcome.

Further, PbO which is one of the essential components in the electro-conductive material of the invention serves not only as a constituent of the double oxide but also as a binder for the crystal component and the glass component. Because of this reason, a resistor composition produced by the use of the electro-conductive material of the invention is provided with an excellent rigidity even when Nb is incorporated for making minus the temperature coefficient of resistivity.

Furthermore, it may be noted that, compared with RuO alone, the double oxide of PbO and Ru0 can be dissolved with ease into a glass component at a high temperature and, when cooled, recrystallized to form a crystallized glass material which is thermally and mechanically stable. The thus obtained resistor composition is assured a good contact of the crystal component and of low resistance.

In addition to the above advantages, it may be also noted that the electro-conductive material of the present invention can be utilized for the formation of a ceramic resistor. Compared with a known carbon solid resistor, the ceramic resistor is much more stable to heat and of a higher wattage.

The electro-conductive material of the present invention essentially consists of PhD and RuO in a molar ratio of 3:1 to 1:3, favorably of 1.5:1 to 1:15. If necessary, less than 50% by mol of PbO and/or of RuO may be replaced by Bi O /2Bi O and H0 respectively. Thus, at least the following four systems may be designed for the electro-conductive material of the invention: (1) PbO-Ru0 (2) Bi O -PbO-RnO (3) PbO-RuO -IrO (4) Bi O -PbO-RuO -IrO For the preparation of the electro-conductive material of the invention, a mixture of the component materials and/or their sources may be sintered, for instance, at a temperature from 400 C. to 1100" C. In the alternative, the electro-conductive material may be produced in a conventional deposition procedure from aqueous solution, if necessary, followed by sintering of the deposited material.

The electro-conductive material of the invention can be used for a wide variety of use. Among them, the use as a resistor paste is one preferred example.

For such use, the electroconductive material is admixed with a glass frit, an organic binder and a solvent. As the electro-conductive material, there may be used the double oxide of any system as above mentioned, if necessary, with replacement of less than 50% by mol' of Ru0 and/or of PhD by TeO W0 V 0 TiO MnO SnO Sb O Sb O CuO, ZnO, Nd O In O Nb O Ta O and/or the like. When a resistor paste of high resistance is desired, there may be employed, for instance, the electro-conductive material wherein Ta O is incorporated as a replaceable oxide. In case of a resistor paste of low resistance being desired, the electro-conductive material wherein Nb O is incoporated as a replaceable oxide may be employed.

Examples of the glass frit are the glass systems of borate, silicate and borosilicate containing at least one of Bi O PbO, A1 ZnO, OdO, alkali metal oxides, alkaline earth metal oxides and rare earth metal oxides. In order to obtain a resistor paste of high resistance, the use of a frit of PbO-B O -SiO system glass is recommended. For obtaining a resistor paste of low resistance, the use of a frit of Bi 0 -Pb0-B O -SiO system glass is preferred.

As the organic binder, there may be used ethyl cellulose, nitrocellulose or the like. Examples of the solvent include organic solvents such as butyl Carbitol, butyl Carbitol acetate and terepineol.

The molar ratio of the electro-conductive material and the glass frit is usually within a range of 0.5 :1 to 0.02:1. In the resistor paste, the combined amount of the organic binder and the solvent normally does not exceed 50% by weight of the total composition.

Another preferred example of the use is a ceramic resistor. Thus, either one of the said systems for the electroconductive material of the invention is sintered, usually at a temperature from 400 C. to 1300 C. to give a ceramic resistor. If desired, any additive such as TeO W03, V205, Tiog, M1102, S1102, Sb O Sbz05, C110, Z110, Nd O In O Nb O Ta O or the like may be incorporated prior to the sintering for regulating the resistivity, the resistance temperature characteristics and the sintering temperature. Among them, the use of Ta O or N-b O is particularly preferred. The amount of the additive to be incorporated may be usually 90% by mol or less on the basis of the combined amount with the electro-conductive material.

Practical and presently preferred embodiments of the present invention are illustratively shown in the following examples.

EXAMPLE 1 Production of electro-conductive material of low resistance (A) PbO-RuO system.In a polyvinyl chloride made pot mill with agate balls, Pb O and RuO in a molar ratio of 3:1 to 1:3 (in terms of PbOzRuo are admixed with water. After evaporation of water, the resultant mixture is admitted in an alumina crucible, heated to 650 C. with a rate of 3 C./min. and calcinated at the temperature for 1 hour to give an electro-conductive material of low resistance as black powder.

When the molar ratio of PhD to RuO' is higher than 1,5, there is remained unreacted PhD in the resulting product. When the molar ratio of RuO to PhD is higher than 1.5, excess of RuO remains as unreacted.

(B) Pbo-RuO -Bi o or IrO system.An electroconductive material is produced according to the same procedure as in (A) but replacing less than 50% by mol of PbO by Bi O or less than 50% by mol of RuO by IrO The resulting product is of low resistance.

In the above procedure, the replacement of more than 50% by mol of PhD by Bi O results unfavorably in growth of the particles of the calcinated product. Further, the sintering of the calcinated product aifords the grown grains.

EXAMPLE 2 Production of glaze resistor paste (A) PbO-RuO glaze resistor paste.The electroconductive material prepared as in Example 1(A) and a irit of lead borosilicate glass (PbO 30% by mol; B 0 45% by mol; SiO 25% by mol; molecular weight, 113.30) in a molar ratio of 0.4 to 0.025:1 are admixed with ethyl cellulose in 1.5% by weight and ot-terepineol in 30% by weight on the basis of the combined weight of the electro-conductive material and the glass frit to give a resistor paste.

The resistor paste is printed in a size of 3 mm. x 3 mm. bridging a pair of silver electrodes provided on an alumina ceramics substrate and fired at a peak firing temperature of 680 C. to 880 C. for 10 minutes with a total cycle of 60 minutes. The sheet resistivity with the peak firing temperature and the molar amount of the electro-conductive material is shown in FIG. 1. The sheet resistivity, the cold temperature coeflicient of resistivity (55 C. to +25 C.), the hot temperature coeflicient of resistivity (+25 C. to +150 C.) and the voltage coefficient of resistivity with the molar amount of the electro-conductive material to 1 mol of the glass component when fired at 760 C. are shown in Table 1.

TABLE 1 Sheet resistivity q) V. C R. (percent/V) From the above table, it is seen that, in case of the molar ratio of the electro-conductive material being small as around 0.05 or less, the resistivity is lowered and the temperature coefiicient of resistivity with positive characteristics is much increased. When the molar ratio is higher than 0.3, the temperature coefiicient of resistivity is positive. At the molar ratio of 0.4, the rigidity of the resistor is inferior.

(B) Glaze resistor paste of high resistance.An electro-conductive material is produced as in Example 1(A) but replacing less than 50% by mol of RuO by Ta O The resulting product becomes grayish with the increase of the T3305 content. The employed T3205 is served partly to form a solid solution with the PbO-Ru0 system double oxide and partly to produce a PbO-Ta 0 system double oxide (e.g. 3PbO-2Ta O The electro-conductive material (0.2 mol) and the glass frit as in (A) (1 mol) are mixed with ethyl cellulose in 1.5 by weight and a-terepineol in 30% by weight on the basis of the combined weight of the electroconductive material and the glass frit to produce a glaze resistor paste.

In the similar manner, there are produced electroconductive materials and glaze resistor pastes using TiO, or SnO in place of Ta O The above obtained glaze resistor pastes are printed and fired as in (A). The sheet resistivity is shown in FIG. 2. The sheet resistivity, the hot temperature coefiicient of resistivity, the cold temperature coefficient of resistivity and the voltage coeflicient of resistivity with the molar ratio of the electro-conductive material to the glass component when fired at 760 C. are shown in Table 2.

The load life test (70 C. in air; resistor size, 3 mm. x 3 mm. squares; substrate size, 10 mm. x '10 mm.; power, /2 -W.; 1% hrs. ON-Vz hr. OFF; after 3000 hrs.), the high temperature exposure test (no load: 150 C. in air; after 3000 hrs.), the short time overload test (1% w. for 5 sec.), the humidity exposure test (40 0.; relative humidity, after 1000 hrs.) and the noise test (using a resistor noise tester model 315 manufactured by Quan. Tech. Laboratories) are carried out, and the results are shown in Table 3.

TABLE 2 T.C.R.( .m. Sheet "03 resistivity V.C.R.

Eleetro-eonduetlve material (molar ratio) (Kn/sq.) Cold Hot (percent/V.)

PbO-RuO; 1:1) 7. 730 +150 +153 -0. 0024 PbO-RuOz-kTazOr (1/0.9 0.1) 09. 53 -101 -86 -0. 0021 Pbo-Ruorl 'lazos 1 0.a 0.2) 998.2 --158 -210 0042 PbO-RuOrZTazOs (1 0.7 0.a a. 25s. 0 -405 -115 -0. 0095 PbO-RuOz-TiOz (1/0.9/0.1) 157. 65 -130 -11s --0. 0035 PbO-RuO SnO (1:0.9:0.1). 10. 874 +165 +135 0. 0022 TABLE 3 AR (percent) High tem- Noise Electra-conductive material (molar Load perature Short time Humidity (dbl ratio) lite exposure overload exposure decade) PbO-RuOq 1:1) 0. 53 0.23 0.02 0.08 -13. Pb0-R11Or.2TazO (1: 0. O8 0. 05 0. 05 3. 8 Pbo-Ruo -l'Tazos (1- 0. 09 0. 07 0. 23 +11. 5 Pb0-RuOz-}Ta2O (1. 0. 19 0.02 0. 21 PbO-RuOz (1:0.9201)..- 0. 27 0. 06 0. +2. 5 PbO-RuOz-SnOz (1:0.9:0.1) 0. 43 0. 08 0. 98 8. 3

From the above tables, it is understood mat the T6815 tors formed as above are excellent in resistance to heat and humidity and quite stable to load.

(0) Glaze resistor paste of low resistance.--An electroconductive material is produced as in Example 1(A) but replacing less than 50% by mol of RuO by Nb O The resulting product becomes grayish with the increase of the x 3 mm. squares; substrate size, 10 mm. x 10 mm.; power, /z w.; 1% hrs. ON== /2 hr. OFF; after 3000 hrs), the high temperature exposure test (no load; 150 C. in air; after 3000 hrs), the short time overload test (1% w. for 5 sec.) and the humidity exposure test (40 C.; relative humidity, 95%; after 1000 hrs.) are carried out, and the results are shown in Table 5.

TABLE 4 '1.C.R. Sheet (p.p.m./ 0.) Noise Molar resistivity V.C.R. (db/ Electro-conduetive material (molar ratio) ratio (Q/sq.) Cold Hot (percent/V) decade) PbO-RuOz-lIZNbQOEO:0.9:0.l) 0. 2 10,832 230 -l86 0. 0023 I3. 5 PbO-RuOzd/ZNbzOAl 0.95:0.05)-. 0.3 796. 4 -35 0. 0016 l9. 5 PbORuO2-1/2Nb O5(1:0.95:0.05) 0. 4 74. 63 +120 +178 0. 0024 --27. 5 Pb0-RuO2-l/2Nb2O O:0.95:0.05) -l- Ag, Pd, Au, Pt 0. 4 31. 88 +321 +270 +0. 0035 -35. 0

1 Of electro-conductive material to glass component.

" TABLE 6 AR (percent) High temperature Short time Humidity Electro-conduetive material (molar ratio) Load life exposure overload exposure PbO-RuOz-%NbzO5(l :0.9:0.1) 0. 37 0. l4 0. 03 0.08 PbO-RuOH/NbzOAl.0.95:0.05) 0. 28 0. 07 0. 02 0. 07 PbO-RuOg-kNbzOafl:0.95:0.05) 0. 27 0. 09 0. 08 0.09 PbO-RuOa-k'ENbZO O:0.95:0.05) plus Ag, Pd, Au, PL- 0. 52 0. 21 0. 13 0. 35

Nb O content. The employed Nb O is served partly to EXAMPLE 3 form a solid solution with the PbO-RuO system double oxide and partly to produce a Pb0-Nb O system double oxide (e.g. 3PbO-2Nb O The electro-conductive material (0.2 mol, and 0.3 mol or 0.4 mol) and a frit of bismuth borosilicate glass (PbO, by mol; %Bi O 10% by mol; B 0 45% by mol; SiO by mol) (1 mol) are mixed with ethyl cellulose in 1.5% by weight a-terepineol in by weight on the basis of the combined weight of the electro-conductive material and the glass frit produces a glaze resistor paste.

Separately, the electro-conductive material (0.4 mol) and the glass frit as above (1 mol) are mixed with 1.5% by weight of ethyl cellulose, 30% by weight of a-terepineol, 5% by weight of silver powder and 5% by weight of noble metal mixtures (Au:Pd:Pt:-=10:3:5 by weight) in the form of a dispersion (Au, 10% by weight; Pr, 3% by weight; Pt, 5% by weight; resin, by weight; solvent, 42 %by weight) on the basis of the combined weight of the electro-conductive material and the glass frit to produce a glaze resistor paste.

The above obtained glaze resistor pastes are printed and tired as in (A). The sheet resistivity is shown in FIG. 3. The sheet resistivity, the hot temperature coeflicient of resistivity, the cold temperature coefiicient of resistivity, the voltage coefiicient of resistivity and the noise with the molar ratio of the electro-conductive material to the glass component when fired at 760 C. are shown in Table 4.

The load life test C. in air; resistor size, 3 mm.

Ceramic resistor (A) Ceramic resistor of low resistance-The electr0 conductive material as prepared in Example 1(A) or 1(B) is admixed with polyvinyl methyl ether in 5% by Weight on the basis of the weight of the electro-conductive material in the presence of water by a wet procedure and, after evaporation of water, the resulting mixture is molded under a pressure of 700 kg./cm. The molded product is heated to 900 C. with a rate of 3 C./ min. and sintered in air at the temperature for 1 hour. The resistivity of the sintered product is shown in Table 6 TABLE 6 Electro-conductive material (molar ratio) Resistivity (Q-cm.)

PbO-RuO 3:1 7.8 10 PbO-Ru0 2:1) 4.8 10 rho-R110, (1:1 3.s 10 Pbo-Ruo 1:2) 7.s 10 PbO-RuO (1:3 6.3 10 PbQ- /zBi O -RuO 0.5:0.s:2 6.3 10 PbO /2Bi O -RuO 0.5:0.5:1 4.6 10 Pbo Bi O -Ruo 1:05:15 7.2 10 PbO-V2Bi O -RuO 2:0.5:1.s 8.3 10- Pbo-RuO -Iro (1:1:1 5.1 10 PbO-RuO -IrO 1:05:05 2.3 10 PbO-RuO -IrO (2:1:05 4.3 10

PbO-RuO -IrO (311:0.5) 9.8)(10 (B) Ceramic resistor.-For :preparation of ceramic resistors of high resistance, there are used electro-conductive materials of PbO-RuO and PbO-RuO -IrO systems wherein RuO or k; is partly replaced by Ta O Nb O TeO W03, V205, T102, M1103, sbgog, SD02, Z110, Nd O 8 4. The electro-conductive material according to claim 1, wherein less than 50% by mol of PhD and of RuO are respectively replaced by Bi O and IrO 5. A resistor paste which comprises the electro-conductive material according to claim 1, a glass frit, an organic 5 or In O whrch are produced from Pb O Ru0 and b1nder andasolvent. various oxides as shown in Table 7 according to the pro- 6. The resistor paste according to claim 5, wherein the cedure as in Example 1(A). But, No.0 is used in the glass frit is a frit of borate, silicate or borosilicate glass form of Nd (CO -8H O. The electroconductive macontaining at least one of B1 0 PbO, A1 0 ZnO, CdO, terial or a mixture of the electro-conductive material (0.8 10 alkali metal oxides, alkaline earth metal oxides are rare mol) and the glass frit (0.2 mol) is admixed with polyearth metal oxides. vinyl methyl ether in 5% by weight on the basis of the 7. The resistor paste according to claim 5, wherein weight of the electro-conductive material or the said m1xthe glass frit is a frit of Bi O -Pb0-B O -SiO system ture in the presence of water by a wet procedure, and the glass. resulting mixture is dried, molded and sintered at 900 C. 5 8. The resistor paste according to claim 5, wherein the for 1 hour. The thus obtained ceramics is shaped in a glass frit is a frit of PbO-B O -SiO system glass. size of 2 mm. x 1 mm x 12 mm., a silver paste is ap- 9. The resistor paste according to claim 5, wherein less phed on both of the opposlte sldes of the longest directhan by mol of RuO in the electro-conductive matetion and fired at 750 0., followed by provldmg a lead rial is replaced by at least one of TeO W0 V 0 SnO wire to make a ceram1c resistor. The temperature co- 2 Sb O Sb O CuO, ZnO, Nd o 11: 0., Ta O and efficient of resistivity and the voltage coeflicient of re- Nb O sistivity are shown in Table 7, and the results of the 10. The resistor paste according to claim 5, wherein load life test, the high temperature exposure test and the less than 50% by mol of RuO; in the electro-conductive short time overload test are shown in Table 8. material is replaced by Nb O TABLE 7 '1.o. Glass Resls- (p.p.m./ G.)

trlt tivity Electro-conductive material (molar ratio) (mol) (0) Hot Cold Poo-13110235151050:0.5:0.5) 0.2 74.43 +940 +490 rbo-nuorwlezorum 0. 2 165. 4 +390 +270 rbo-Ruorl'rmoi 1:0 0.2 355.4 +95 +27 PbO-RuOa-Vz'TazOa 1:0 0.2 1.7855 -430 -325 PhD-11110746103201 1.5. .0.7) 0.2 168.1 +300 +280 PbO-RuO -}*Nbz0:(1:0.3:0 7 0. 2 135. 2 -352 -270 PbO-RuOrSuO7(1.0.3.0. 0. 2 355. 4 +210 -451 Poo-35mm:- 0. 2 353. 1 -517 -482 PbO-%Biz0s-R110z-%TflzOs(120.5:0 3-0 0. 2 455. 3 -305 -280 Pbo-Ruor;/2Te.0:-%vo.(1:03:0.5: None 15. 43 +1. 581 +1. 945 Pbo-Ruo:-9Te:o:-wo: 1: None 35.42 +974 +651 PbO-RuOH/TazOw SbzO None 43. 52 +082 +783 PbO-RuO 'TazOs-MnOz None 4535 +135 +232 PbO-RuOrYiTMOs-TGOKI: None 27.31 +070 +573 PbO-RuOzJTazOrTiOzO: None 58. 35 +435 070 Pb0-0u0-Ru0r'110:(0.9: 0.2 1.538 -1. 510 -1.315 Pb0-%Nd:0:-Ru0rsno:(0. 0. 2 425. 3 -015 -537 PbO-ZnO-RuOrVz'TazOKOBzO 0. 2 235. 4 +420 +355 Pb0-%InzO:-RuOg-%Taz05((l.9: 0.2 15.473 1.315 -1.255

R (percent) Hi Glass tempera- Short frit Load t time (mol) life exposure overload 0.2 0.23 0.35 0.23 Pbo-Rum-sno: (1:0. 3:0. 7) 0. 2 0. 95 0. 32 0. 54 PbO-eBi2O -Ru0Z-%T82o5 (0. 5:0. 5:0. 3:0. 7). 0. 2 0. s3 1. 23 0. 71 Pb0-9Biz0 -Ru0z-3'1sz0: (1 :0. 5 :0. 3:0. 7) 0. 2 0.13 0.13 0. 02 Pb0-Ru0:-%Ta:0:- /V:0: (1:0.3z0. 2.37 1.25 0.16 rbo-nuoz- /rezoi-wo (1:0.3:0. 3: 1.03 1.13 0.75 Pb0-Ru0r TazO5-%Sbz0 (1: 3- 0. 87 0.52 0.42 PbO-RHOrPfiTMDg-MnOz 1: 0. 95 0. s3 0. 23 Pbo-Ruo2-%Ta:0:-Teo: (1 :0. 0. 72 o. 53 0. 28 PbO-RuOz /fiTMOs-TIO: (1: :.1)- None 2.10 1.01 0.37 PbO-CuO-RuOz-TiOz 0.9:0.1:0.3:0.5)---.. 0. 2 1. 35 1. 42 0. PbO-%NdzO RuOrSnO2 (0. 9:0. 1:0. 3:0. 5).-- 0. 2 0.98 1. 21 0. 72 PbO-ZnO-RuO2-%Ta205 (0. 9:0. 1:0. 3:0. 0).... 0. 2 2. 35 2. 7s 1. 05 PbO-%InzO -RuO2-%TazO (0. 9:0. 1:0. 3:0. 5) 0. 2 4 51 3. 23 1. 7s

N0'1E. (1) Load Ilfe test=% w., C., 1.5 hrs. 0N-0.5 hr. OFF, after 3,000 hrs. (2) Hlg temperature exposure test=150 w., air, after 3,000 hrs. (3) Short time overload test=lM w.;

11. The resistor paste according to claim 5, wherein less than 50% by mol of Ru0 in the electro-conductive material is replaced by Ta O 12. The resistor paste according to claim 5, wherein the molar ratio of the electro-conductive material and the glass frit is 0.5 :1 to 0.02: 1.

13. The resistor paste according to claim 5, wherein at least one of noble metals and their organic compounds is incorporated.

14. The resistor paste according to claim 13, wherein the noble metal is Ag, Pd, Pt, Au, Rh, Ru or Ir.

15. An electro-conductive material according to claim 1, wherein less than 50% by mol of RuO is replaced by T3205.

16. The resistor paste according to claim 5, wherein less than 50% by mol of PbO in the electro-conductive material is replaced by at least one metal oxide selected from the group consisting of Bi O TeO W05, V S1102, Sb203, Sb205, C110, ZnO, Nd203, T3205 and Nb205.

.17. The resistor paste according to claim 5, wherein less than 50% by mol of PhD and of RuO are, respectively, replaced by a metal oxide selected from the group Consisting Of T60 W03, V205, SD02, $13203, $13205, ZnO, Nd O In O Ta 0 and Nb O wherein the metal oxides respectively replacing said PbO and RuO are the same or difierent.

18. A ceramic resistor which comprises a ceramic body comprising the electro-conductive material according to claim 1 which has been fired.

19. The ceramic resistor according to claim 18, wherein less than 50% by mol of Ru0 in the electro-conductive material is replaced by at least one of TeO W0 V 0 T102, MnO Sn0 Sb O Sb O CuO, ZnO, Nd O 111 03, T3205 and N13205- 20. The ceramic resistor according to claim 18, wherein less than 50% by mol of RuO in the electro-conductive material is replaced by Ta O 21. The ceramic resistor according to claim 18, wherein less than 5 0% by mol of Ru0 in the electro-conductive material is replaced by Nb O 22. The ceramic resistor according to claim 18, wherein less than 50% by mol of RuO and of PhD in the 10 electro-conductive material are respectively replaced by Nb 05 and Bi O 23. The ceramic resistor according to claim 18, wherein less than by mol of Ru0 and of PbO in the electro-conductive material are respectively replaced by T3205 and Bi203- 24. The ceramic resistor according to claim 18, wherein less than 50% by mol of PhD in the electro-conductive material is replaced by at least one of Bi O TeO W0 V205, S1102, Sb O- 813 05, C110, ZnO, Nd O T3205 and Nb O 25. The ceramic resistor according to claim 18, wherein less than 50% by mol of PhD and of RuO are, respectively, replaced by Te0 W0 V 0 SnO Sb O Sb O CuO, ZnO," Nd O In O Ta O and Nb O wherein the metal oxides respectively replacing said PbO and RuO are the same or different.

References Cited UNITED STATES PATENTS 3,373,119 3/1968 Krystyniak 2525 18 3,352,797 11/1967 Kim 252--518 3,304,199 2/1967 Faber, Sr. et al 2525 18 3,324,049 6/1967 Holmes 252-5'18 3,044,901 7/ 1962 Garnsworthy 2525 18 2,950,996 8/1960 Place, Sr. et a1 2525l8 3,052,573 9/ 1962 Dumesnil 252-5 18 3o GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner US. Cl. X.R. 117--201; 25-2--5l8 

